Moderna (MRNA 0.42%) announced today that it has completed enrollment in the 30,000-participant study of mRNA-1273, the company's vaccine designed to protect against the novel coronavirus that causes COVID-19.

The biotech slowed enrollment toward the end of the study because it was specifically recruiting minorities to increase the diversity of participants in the clinical trial. In the end, the study enrolled 37% minorities, similar to the diversity of the U.S. population. Diversity is important because people with different genetic and environmental backgrounds could be affected by the vaccine differently.

Gloved hand giving an injection into a shoulder

Image source: Getty Images.

Moderna still beat Pfizer (PFE -3.07%) and BioNTech (BNTX -3.23%) to the finish line, but that's only because the duo pushed out the goal for their study from 30,000 to 44,000 participants. As of Monday, the companies had enrolled 39,862 participants in the clinical trial testing their coronavirus vaccine BNT162b2. The study includes 43% minorities, although some of those diverse participants came from outside the U.S.

In addition to diversity, it's important for the studies to look at older patients and those with high-risk chronic diseases, since they're at increased risk of severe COVID-19. Moderna's study includes more than 7,000 Americans over the age of 65 and 5,000 Americans who are under the age of 65 but have high-risk chronic diseases. All told, 42% of the participants are in medically high-risk groups.

At this point there's nothing left to do but wait and see if more people in the study who received placebo end up developing COVID-19 relative to the people who received the vaccine. As fate would have it, since the study is designed to determine efficacy after a certain number of COVID-19 cases, the surge in cases that the U.S. is currently experiencing will result in the data being produced sooner than if the infection rate were lower.